Stop using a singleton for routes

This change ensures we're no longer using a singleton for routes because
we want to change the routing table based on the controller we're
testing. We don't want the routing table to be global for the Action
Pack tests.

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

actionpack/test/abstract_unit.rb

@@ -69,7 +69,10 @@ end
 module ActionDispatch
   module SharedRoutes
     def before_setup
-      @routes = SharedTestRoutes
+      @routes = Routing::RouteSet.new
+      ActiveSupport::Deprecation.silence do
+        @routes.draw { get ":controller(/:action)" }
+      end
       super
     end
   end